1. Field of the Invention
The present invention relates to a vehicle occupant discriminating apparatus for discriminating an occupant on a vehicle seat based on the load applied to the vehicle seat.
2. Description of the Related Art
Such a vehicle occupant discriminating apparatus is used for determining whether an occupant is seated on a front passenger seat where an airbag system is provided, for example. That is, if no occupant is seated on the front passenger seat, operation of the airbag system is meaningless and expenses are necessary for its recovery, so that the airbag system is operated based on the determined result. It is more effective to change the airbag operation method, such as airbag inflation speed and direction, and to operate the airbag or not, on the basis that the sitting occupant is an adult or child and the occupant is large or small in pattern. Thus, it is very preferable that the vehicle occupant discriminating apparatus discriminate not only whether an occupant is seated but also discriminate the occupant including his or her physical constitution.
Various kinds of such a vehicle occupant discriminating apparatus have been proposed, and in Japanese Unexamined Patent Application Publication No. H09-207638 (first to sixth and eighteenth and nineteenth paragraphs, FIGS. 1 and 5), an apparatus capable of securely detecting the presence of an occupant is disclosed, for example. In the occupant detecting apparatus in the Publication, load sensors are provided at only two positions among multiple (four usually) fitting positions between a vehicle seat and a floor. This means that the load sensors are only attached to any two positions of the four seat-fitting positions that are lateral, back-and-forth, and diagonal positions. This apparatus can clearly distinguish between a vacant state and an occupied state even when the load sensors are attached to any of the positions.
In Japanese Unexamined Patent Application Publication No. 2003-341403 (second, fourteenth to sixteenth, twenty-third, thirty-second, and thirty-ninth paragraphs, FIGS. 4 to 7), an apparatus that can precisely detect the kind of an occupant (adult, child, or vacant) on a seat is also disclosed. In this apparatus, by adding up detected respective load values from load sensors arranged at four lateral and back-and-forth positions below the vehicle seat, a total load is calculated. Then, on the basis of the total load, the kind of the occupant (adult, child, or vacant) is determined so as to output a drive signal for changing the inflation amount of the airbag system, for example, on the basis of the kind of the occupant.
In the apparatus of Japanese Unexamined Patent Application Publication No. 2003-341403, the precise occupant detection is achieved; however, four load sensors are used therefor. On the other hand, the apparatus of Japanese Unexamined Patent Application Publication No. H09-207638 can work with two load sensors; however, it can detect the presence of an occupant but cannot determine the kind of the occupant. That is, in any of the above prior arts, the reduction in the number of the load sensors is incompatible with the precise determination of an occupant even to its kind.
When the load sensors at the four positions are used for detecting the load on the vehicle seat, the load is not be applied to the four positions uniformly in general. In the vehicle seat, while the front portion is slightly raised, the rear portion is slightly sunk so as to have a structure capable of easily resting oneself on a seat back. Hence, the occupant load is mainly applied to the rear portion. Then, the load sensors may be provided only on the rear lateral positions; however, if a child is standing on the seat, the load is concentrated only on the rear portion so that a minus load may be applied to the front portion. If the load sensors are arranged only on the rear side at this time, since the minus load on the front side is not added, a large load is mistakenly detected consequently. As a result, a child on the vehicle seat may be determined to be an adult.